1. Field of the Invention
The present invention relates to optical gas sensing apparatuses.
2. Description of Related Art
For example, Japanese Unexamined Patent Publication H8-184556 discloses an optical gas sensing apparatus, which includes a light source (light emitting member) and a light sensing element (light receiving member). This optical gas sensing apparatus detects a concentration of measured gas based on an absorbance of light due to the measured gas, which is introduced to a light passage of the light emitted by the light source.
In order to effectively use a light intensity from the light source, a general optical gas sensing apparatus includes a tubular housing member, an inner surface of which reflects the light so that the light is converged to the light sensing element. Also, in order to facilitate assembly and maintenance, the light source and/or the light sensing element are/is mounted on the housing member. Typically, the light source is mounted on a light source member, which caps one end of the housing member. Also, the light sensing element is mounted on a light sensing member, which caps another end of the housing member. Thereby, a closed space is defined by the housing member, the light source member and the light sensing member. The measured gas is introduced to this closed space so that the absorbance of the light, which is absorbed by the measured gas, is sensed by the light sensing element. Thus, the concentration of the measured gas is sensed. Here, the light is emitted by the light source.
In the above structured conventional optical gas sensing apparatus, in order to limit a change of a sensor output, screws are used to fix the housing member and the light source member, and to fix the housing member and the light sensing member instead of press fitting and snap fitting, which may cause erroneous allocation or displacement in some cases. However, the assembly by use of the screw may increase a number of components and a man hour. Thus, a production cost may increase.